62 BARBOUR: ZOOGEOGRAPHY. 



. But we have not yet mentioned really the half of the peculiarities of this 

 amphibian fauna; for amongst the Ranidae we find a remarkable autogenous 

 genus, so far known only from Faro Island, — Batrachylodes vertebralis Blgr. ; 

 and upon all of the islands, with the exception of San Cristoval, we find a ranid- 

 derivative so differentiated as to constitute the type of a peculiar family, the 

 single known species being Ceratrobatrachus guentheri Blgr. It is interesting 

 to note that hitherto every island explored, with the exception of the one men- 

 tioned, which was probably separated very early from the rest of the group, 

 supports this pecuUar creature; but it is still more remarkable that from the 

 different islands as we know them now there does not seem to be any peculiar 

 local differentiation amongst the various individuals. This may perhaps be 

 due to the fact that the form itself seems to be an especially variable one. 

 Three pecuUar species of Hyla close the list. 



